[Synthetics] add monitor id migration

[dominiqueclarke]

Summary

Relates to #143309

Adds a migration to add two fields to each monitor saved object

1. [ConfigKey.HEARTBEAT_ID] ('id') - The id to use for ES queries to heartbeat. Either the saved object id for UI monitors, or the custom heartbeat id for project monitors. This new key can be used regardless of monitor type as the single source of truth as the id to use for ES queries
2. [ConfigKey.CONFIG_ID] ('config_id') - This id is always the saved object id. It is an exact match to savedObject.id. I've added this key as a way to perform aggregations against the monitor saved object id in the future, as it's currently impossible to do terms aggregations against savedObject.id but possible to do aggregations os any field within the savedObject attributes. By moving a copy of the id into the saved object attributes, we can perform aggregations if needed in the future.

This PR is a prerequisite for standardizing the use of ConfigKey.HEARTBEAT_ID across the app. Making use of these new keys in a predictable, standardized way will take place in a subsequent PR.

Testing

1. Checkout the 8.5 branch before pulling down this PR. (Note, you'll want to do this while running ES locally, instead of using a edge oblt ES. If your edge oblt ES is on an older ES version than 8.6, the migration won't go through)
2. Create 1 of each monitor for both UI and project monitors
3. Checkout this PR
4. Navigate to the Monitor Management page and find the get request for monitors
5. View each monitor's id and config_id value. For project monitors, the id value should match custom_heartbeat_id. For ui monitors, the id value should match the saved object id. For both monitor types, the config_id value should match the saved object id.

[dominiqueclarke]

@elasticmachine merge upstream

[elasticmachine]

Pinging @elastic/uptime (Team:uptime)

[dominiqueclarke]

@elasticmachine merge upstream

[shahzad31]

so we need migration to get rid of this?

[shahzad31]

Let's do follow up to clean up the usage of the field !!

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: 8c790db

Metrics [docs]

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
synthetics	1.0MB	1.0MB	+156.0B

Unknown metric groups

ESLint disabled in files

id	before	after	diff
osquery	1	2	+1

ESLint disabled line counts

id	before	after	diff
enterpriseSearch	19	21	+2
fleet	58	64	+6
osquery	106	111	+5
securitySolution	440	446	+6
total			+19

Total ESLint disabled count

id	before	after	diff
enterpriseSearch	20	22	+2
fleet	66	72	+6
osquery	107	113	+6
securitySolution	517	523	+6
total			+20

History

• 💚 Build #85105 succeeded 9e62978
• 💔 Build #84540 failed 191490a
• 💔 Build #84527 failed 178bfa1
• 💚 Build #84484 succeeded d7a5fa9
• 💛 Build #83985 was flaky 64c9fe6
• 💚 Build #83592 succeeded cef4828

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

[shahzad31]

POST FF Testing, tested this on cloud staging

1. Created 8.5.2 deployment
2. Added a monitor, verified attributes.id field is empty
3. Upgraded to 8.6, field is populated now with so id